Cocoa flavanols

What it is

Cocoa flavanols are plant compounds found in cocoa, sold as cocoa extract capsules, high-flavanol cocoa powders and dark chocolate. The largest trial describes cocoa extract as a source of flavanols, and gave a daily extract containing 500 mg of flavanols. How much a cocoa powder contains depends on processing: alkalizing ('Dutch processing') removes much of it.

What the research says

The best evidence is a Cochrane review of short trials (2 to 18 weeks) finding a small drop in blood pressure of about 2 mmHg, rated moderate quality, with a significant drop in people with high blood pressure and no significant drop in people with normal blood pressure, although the review says the difference between those groups was only of borderline significance (P = 0.08) and needs confirming. EFSA in 2012 accepted that 200 mg a day of cocoa flavanols helps maintain blood-vessel widening (endothelium-dependent vasodilation). The large COSMOS trial (21,442 older adults, 3.6 years) found no significant reduction in its main outcome of total cardiovascular events, although cardiovascular deaths were lower, a secondary result. COSMOS sub-studies found no effect on cancer or on cognition overall. The main safety concern is lead and cadmium in some cocoa products.

Evidence grade: Limited evidence.

What goes wrong

Across trials, cocoa products caused few side effects: gastrointestinal complaints and nausea in about 1% on cocoa versus 0.4% on control. (Source 1)

• Systematic review, Moderate certainty.
• Size: 1,804 participants.
• Who: Mainly healthy adults.
• How long: 2 to 18 weeks.
• Result: Adverse effects 1% (cocoa) vs 0.4% (control)
• Funding: Independent Cochrane review.

Generally, cocoa products were highly tolerable, with adverse effects including gastrointestinal complaints and nausea being reported by 1% of participants in the active cocoa intervention group and 0.4% of participants in the control groups

Laboratory testing of 72 US cocoa products bought 2014 to 2022 found 43% exceeded California Prop 65 daily limits for lead and 35% for cadmium, with organic products more likely to be higher. (Source 2)

• Survey study, Low certainty.
• Size: 72 products.
• Who: Consumer dark chocolate and cocoa products in the USA.
• How long: Products bought in 2014, 2016, 2019 and 2022.
• Result: 43% over Prop 65 MADL for lead, 35% for cadmium, 0% for arsenic; 97.2% below FDA interim reference level for lead.
• Funding: Authors declared no funding; one co-author (Tod Cooperman) leads ConsumerLab.com, which did the testing.

Our analysis reports that 43%, 35%, and 0% of the products tested exceed Prop 65 MADLs for heavy metal concentrations, respectively, of Pb, Cd, and As

The same analysis judged that a single serving of most products posed little risk, but several servings a day plus other sources could exceed the limits. (Source 2)

• Survey study, Low certainty.
• Size: 72 products.
• Who: Consumer cocoa products.
• How long: 2014 to 2022.
• Result: Median metal levels below Prop 65 limits; outliers drove the exceedances.
• Funding: No funding declared.

consuming some of the products tested, or more than one serving per day in combination with non-cocoa derived sources heavy metals, may add up to exposure that would exceed the Prop 65 MADLs

COSMOS reported no safety concerns with 500 mg a day of cocoa flavanols over a median 3.6 years. (Source 3)

• Randomized trial, Moderate certainty.
• Size: 21,442 adults.
• Who: Older US adults.
• How long: Median 3.6 years.
• Result: No safety concerns reported.
• Funding: NIH plus Mars Edge.

Per-protocol analyses censoring follow-up at nonadherence supported a lower risk of total cardiovascular events (HR: 0.85; 95% CI: 0.72, 0.99). There were no safety concerns.

What the evidence supports

A Cochrane review found flavanol-rich cocoa products lowered blood pressure by a small amount in short trials, with moderate-quality evidence. (Source 1)

• Systematic review, Moderate certainty.
• Size: 1,804 participants across 40 treatment comparisons.
• Who: Mainly healthy adults.
• How long: 2 to 18 weeks (mean 9 weeks)
• Result: Systolic MD -1.76 mmHg (95% CI -3.09 to -0.43); diastolic MD -1.76 mmHg (95% CI -2.57 to -0.94); about 2 mmHg overall.
• Funding: Independent Cochrane review; the review notes some trials were industry-supplied (not quoted here)

chocolate and cocoa products cause a small (2 mmHg) blood pressure

EFSA (2012) concluded that cocoa flavanols help maintain endothelium-dependent vasodilation at 200 mg a day, on an application from the cocoa company Barry Callebaut. (Source 4)

• Official position, Certainty not rated.
• Size: Based on several human intervention studies, the key one lasting 12 weeks.
• Who: General population.
• How long: Position dated 2012.
• Result: Health claim authorised for 200 mg cocoa flavanols per day.
• Funding: Industry application (Barry Callebaut); assessed by EFSA NDA Panel.

The Panel concludes that a cause and effect relationship has been established between the consumption of cocoa flavanols and maintenance of normal endothelium-dependent vasodilation.

What the evidence does not support

Cocoa did not significantly lower blood pressure in people whose blood pressure was already normal, while systolic pressure fell significantly in people with high blood pressure; however, the review says the difference between these groups was only of borderline significance and needs further research to confirm. (Source 1)

• Systematic review, Moderate certainty.
• Size: 1,063 participants in 23 comparisons (normotensive); 401 in 9 comparisons (hypertensive)
• Who: Normotensive, prehypertensive and hypertensive adults.
• How long: 2 to 18 weeks.
• Result: Systolic reduced about 4 mmHg in hypertensive people; no significant difference in normotensive people; test for subgroup differences P = 0.08 (borderline)
• Funding: Independent Cochrane review.

Limit of this finding: The review did not show that cocoa works better in people with high blood pressure than in people with normal blood pressure. The statistical test comparing these groups was not conventionally significant (P = 0.08), and the authors say further research is needed to confirm it. Treat the bigger drop seen in people with high blood pressure as a possibility, not an established difference.

there was no significant difference in normotensive people (n = 23 treatment comparisons, 1063 participants); however, the test for subgroup differences was of borderline significance (P = 0.08

In the COSMOS trial, cocoa extract did not significantly reduce total cardiovascular events, the primary outcome, in older adults. (Source 3)

• Randomized trial, Moderate certainty.
• Size: 21,442 US adults.
• Who: Women 65 and over and men 60 and over, free of major cardiovascular disease.
• How long: Median 3.6 years.
• Result: Total cardiovascular events 410 vs 456; HR 0.90 (95% CI 0.78 to 1.02; P = 0.11)
• Funding: NIH (NHLBI, NIA, NEI) plus Mars Edge (industry; cocoa extract maker)

Cocoa extract supplementation did not significantly reduce total cardiovascular events among older adults but reduced CVD death by 27%.

In COSMOS, cocoa extract had no significant effect on cancer. (Source 5)

• Randomized trial, Moderate certainty.
• Size: 21,442 adults (COSMOS)
• Who: Older US adults.
• How long: Median 3.6 years.
• Result: No significant effect on total invasive cancer, individual cancers or cancer death (as reported by the trial website)
• Funding: NIH plus Mars Edge.

Participants taking cocoa extract experienced no significant effects on total invasive cancer, individual cancers, or cancer death.

COSMOS cognition sub-studies found cocoa extract did not affect cognition at their primary time points. (Source 5)

• Randomized trial, Moderate certainty.
• Size: COSMOS-Mind and COSMOS-Web subsets of COSMOS (numbers not captured from the fetched page)
• Who: Older US adults.
• How long: 1 year primary timepoint (COSMOS-Web)
• Result: No effect on the prespecified primary cognition outcome.
• Funding: NIH plus Mars Edge.

cocoa extract supplementation did not affect the prespecified primary timepoint of cognition at 1 year

Where the evidence is mixed

In the same Cochrane review, the evidence was downgraded from high to moderate because of unexplained differences between trials. (Source 1)

• Systematic review, Moderate certainty.
• Size: 1,804 participants.
• Who: Mainly healthy adults.
• How long: 2 to 18 weeks.
• Result: Quality rating reduced to moderate for heterogeneity.
• Funding: Independent Cochrane review.

we downgraded the quality of the evidence from high to moderate

COSMOS found lower cardiovascular death with cocoa extract as a secondary outcome, and a lower risk of total events in a per-protocol analysis; the authors said more research is needed. (Source 3)

• Randomized trial, Low certainty.
• Size: 21,442 adults.
• Who: Older US adults.
• How long: Median 3.6 years.
• Result: CVD death HR 0.73 (95% CI 0.54 to 0.98); per-protocol total events HR 0.85 (95% CI 0.72 to 0.99); all-cause mortality HR 0.89 (95% CI 0.77 to 1.03)
• Funding: NIH plus Mars Edge.

Additional research is warranted to clarify whether cocoa extract may reduce clinical cardiovascular events.

Where the research disagrees

Whether cocoa flavanols protect the heart

• EFSA NDA Panel, 2012, Short human intervention studies of a blood-vessel marker (flow-mediated dilation): The Panel concludes that a cause and effect relationship has been established between the consumption of cocoa flavanols and maintenance of normal endothelium-dependent vasodilation. (Source 4)
• COSMOS investigators (Sesso et al., 2022), Large randomized trial with clinical events: Cocoa extract supplementation did not significantly reduce total cardiovascular events among older adults but reduced CVD death by 27%. (Source 3)

How much

• Reference intake: No RDA or AI exists for cocoa flavanols; they are not an essential nutrient. EFSA (2012) stated 200 mg of cocoa flavanols a day is needed for its authorised vasodilation claim. (Source 4)
• Upper limit: No tolerable upper intake level for cocoa flavanols was found in the sources reviewed. The largest trial (500 mg flavanols a day for a median 3.6 years) reported no safety concerns. Heavy-metal exposure from cocoa products is judged against California Prop 65 limits, not a flavanol limit. (Source 3)
• Studied: COSMOS gave a cocoa extract providing 500 mg flavanols a day, including 80 mg epicatechin, for a median 3.6 years. (Source 3)
• Studied: Cochrane blood pressure trials used flavanol-rich chocolate and cocoa products for 2 to 18 weeks. (Source 1)

A common belief, and what the research shows

The belief: Eating chocolate is a proven way to prevent heart attacks and strokes.

What the research shows: The largest trial of concentrated cocoa flavanols found no significant reduction in total cardiovascular events: 'Cocoa extract supplementation did not significantly reduce total cardiovascular events among older adults but reduced CVD death by 27%.' The blood pressure effect in short trials is small: 'chocolate and cocoa products cause a small (2 mmHg) blood pressure' lowering effect. Heavily processed (Dutched) cocoa loses most of its flavanols.

Questions and answers

What is it?

Cocoa flavanols are plant compounds in cocoa. Supplements sell them as cocoa extract; the largest trial used an extract giving 500 mg of flavanols a day. (Source 3)

What does it do in the body?

In short trials they slightly lower blood pressure, by about 2 mmHg on average, with a larger drop seen in people with high blood pressure, although the review says that difference between groups was only borderline and not yet confirmed. EFSA accepts that they help blood vessels widen normally. A large 3.6-year trial did not show a significant drop in total heart and stroke events. (Source 1)

Is it good or bad for you?

Mostly neutral to mildly helpful for blood pressure, with few side effects (about 1% had stomach complaints in trials). The main risk is lead and cadmium in some cocoa products, which can add up with several servings a day. (Source 1)

How do you get more of it?

Trials used cocoa extract supplements or flavanol-rich cocoa products. EFSA said 200 mg a day could come from 2.5 g of high-flavanol cocoa powder or 10 g of high-flavanol dark chocolate. (Source 4)

If it is harmful, what reduces it?

Does not apply to the flavanols themselves. The harmful part can be heavy metals in some cocoa products; testing found median levels were below limits, with a minority of products driving the excess. (Source 2)

Why might someone be low in it or missing it?

Cocoa flavanols come only from cocoa, so people who eat little cocoa get little. Processing matters: alkalizing (Dutching) cocoa powder strips most of the flavanols. (Source 6)

Which whole foods contain it or feed it?

Cocoa powder and dark chocolate. Natural (non-alkalized) cocoa keeps the most; heavily Dutched cocoa keeps about 10%. (Source 6)

What happens if you do not have it?

Nothing specific is known to happen: cocoa flavanols are not an essential nutrient and no deficiency disease exists. In the large trial, adding them did not significantly change total cardiovascular events, cancer, or cognition overall. (Source 5)

How can you test for it?

No routine clinical test for cocoa flavanol status was found in the sources we fetched. Research studies use urine flavanol metabolite markers, but we could not reach a source describing them. (Source 5)

We searched: WebSearch for COSMOS cognition and flavanol biomarkers; cosmostrial.org results page; Alzforum and Wiley pages were blocked (403)

References

1. Cochrane Database of Systematic Reviews. Effect of cocoa on blood pressure. 2017. PMID 28439881, DOI 10.1002/14651858.CD008893.pub3. Read the source
2. Frontiers in Nutrition. A multi-year heavy metal analysis of 72 dark chocolate and cocoa products in the USA. 2024. DOI 10.3389/fnut.2024.1366231. Read the source
3. The American Journal of Clinical Nutrition. Effect of cocoa flavanol supplementation for the prevention of cardiovascular disease events: the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized clinical trial. 2022. PMID 35294962, DOI 10.1093/ajcn/nqac055. Read the source
4. EFSA Journal (EFSA Panel on Dietetic Products, Nutrition and Allergies). Scientific Opinion on the substantiation of a health claim related to cocoa flavanols and maintenance of normal endothelium-dependent vasodilation pursuant to Article 13(5) of Regulation (EC) No 1924/2006. 2012. DOI 10.2903/j.efsa.2012.2809. Read the source
5. COSMOS trial investigators (Brigham and Women's Hospital). Results - COSMOS Trial (COcoa Supplement and Multivitamin Outcomes Study). 2024. Read the source
6. EurekAlert! (news release). New study re-emphasizes natural cocoa powder has high antioxidant content (news release on Miller et al., Impact of Alkalization on the Antioxidant and Flavanol Content of Commercial Cocoa Powders, J Agric Food Chem 2008). 2008. DOI 10.1021/jf801670p. Read the source